Rapid response fuel cell system

Abstract

Method and apparatus for supplying extra/booster steam and/or fuel vapor to the fuel processor of a fuel cell system during surges in power demanded from the fuel cell. Hot water and/or liquid fuel is/are stored under pressure until needed. When needed during power surges, the pressure is rapidly reduced on the hot liquid(s) causing it/them to flash vaporize and supplement the normal, steady state supply of steam/fuel-vapor to the fuel processor.

1. In a fuel cell system comprising a fuel cell that consumes hydrogen in the electrochemical production of electricity, a fuel processor for producing said hydrogen from a hydrogen-containing fuel and steam, and a steam vaporizer for converting water into said steam and supplying a first quantity of said steam to said fuel processor at a first pressure, wherein the improvement comprises a steam buffer communicating with said fuel processor in parallel with said steam vaporizer for supplying a second quantity of steam to said fuel processor during surges in the electrical power demanded from said fuel cell system, said steam buffer comprising a vessel containing a pool consisting essentially of water under a second pressure greater than said first pressure and at a temperature greater than the boiling point of water at said first pressure, a pump for supplying water to said vessel at said second pressure, a heat exchanger for heating said water to said temperature, an inlet valve communicating said pump with said vessel, an outlet valve communicating said vessel with said fuel processor, and a controller for closing said inlet valve and opening said outlet valve during said surges to rapidly reduce the pressure in said vessel so as to cause said water in said pool to flash vaporize and provide said second quantity. 
     
     
       2. In a fuel cell system comprising a fuel cell that consumes hydrogen in the electrochemical production of electricity, a fuel processor for producing said hydrogen from a liquid, hydrogen-containing fuel and water, and a fuel vaporizer for converting said hydrogen-containing fuel to a vapor and supplying a first quantity of said vapor to said fuel processor at a first pressure, wherein the improvement comprises a fuel buffer communicating with said fuel processor in parallel with said fuel vaporizer for supplying a second quantity of fuel vapor to said fuel processor during surges in the electrical power demanded from said fuel cell system, said fuel buffer comprising a vessel containing a pool of fuel consisting essentially of said liquid hydrogen-containing fuel under a second pressure greater than said first pressure and at a temperature greater than the dew point of said hydrogen-containing fuel at said first pressure, a pump for supplying said liquid hydrogen-containing fuel to said vessel at said second pressure, a heat exchanger for heating said liquid hydrogen-containing fuel to said temperature, an inlet valve communicating said pump with said vessel, an outlet valve communicating said vessel with said fuel processor, and a controller for closing said inlet valve and opening said outlet valve during said surges to rapidly reduce the pressure in said vessel so as to cause said liquid hydrogen-containing fuel in said pool to flash vaporize and provide said second quantity. 
     
     
       3. A method of operating a fuel cell system having a fuel cell that consumes hydrogen in the electrochemical production of electricity and a fuel processor for producing said hydrogen from a hydrogen-containing fuel and water, comprising the steps of vaporizing said water to provide a first quantity of steam to said fuel processor at a first pressure when operating said fuel cell at a first power level, and supplying a second quantity of steam to said fuel processor in parallel with said first quantity to supplement said first quantity during surges in the electrical power to a higher power level than said first power level by providing a pool consisting essentially of water at a second pressure greater than said first pressure and at a temperature greater than the boiling point of water at said first pressure and rapidly reducing the pressure on said pool during said surges from said second pressure to said first pressure to flash vaporize the water in said pool and provide it to said fuel processor. 
     
     
       4. A method according to  claim 3  comprising replenishing said pool by providing a two phase mixture of water and steam to said vessel between said surges. 
     
     
       5. A method according to  claim 3  wherein said temperature is the boiling point at about said second pressure. 
     
     
       6. A method according to  claim 4  including bubbling steam supplied to said vessel through said pool to heat said pool between said surges. 
     
     
       7. A method of operating a fuel cell system having a fuel cell that consumes hydrogen in the electrochemical production of electricity and a fuel processor for producing said hydrogen from a liquid, hydrogen-containing fuel and water, comprising the steps of vaporizing said fuel in a fuel vaporizer to provide a first quantity of fuel vapor to said fuel processor at a first pressure when operating said fuel cell at a first power level, and supplying a second quantity of fuel vapor to said fuel processor in parallel with said fuel vaporizer to supplement said first quantity during surges in the electrical power to a higher power level than said first power level by providing a pool of fuel consisting essentially of said liquid, hydrogen-containing fuel at a second pressure greater than said first pressure and at a temperature greater than the dew point of said fuel at said first pressure, and rapidly reducing the pressure on said pool from said second pressure to said first pressure to flash vaporize the fuel in said pool and provide it to said fuel processor. 
     
     
       8. A method according to  claim 7  comprising replenishing said pool by providing a two phase liquid-vapor mixture of said fuel to said vessel between said surges. 
     
     
       9. A method according to  claim 8  including bubbling fuel vapor supplied to said vessel through said pool to heat said pool between said surges. 
     
     
       10. A method according to  claim 7  wherein said temperature is the bubble point at about said second pressure.